This invention relates to the patterning of metallic, insulator, and semiconductor thin films by controlled removal for use in large area electronics.
The production of large area electronic devices utilizing organic semiconductor films typically requires the spatial patterning of various materials over a large area substrate. These films must also possess precisely defined thicknesses to ensure device and system functionality. Large area electronics typically utilize non-semiconductor substrates such as glass, plastic, metal foil, or ceramic and may be rigid or flexible. Such electronic devices are utilized in a number of product applications, including displays, lighting components, photovoltaics, sensors, and identification tags. Displays may be utilized in a number of settings, including televisions, mobile phones, signage, cameras, computers, global positioning systems, and gaming devices. The organic semiconductor films and ail layers that are deposited above them cannot be patterned by photolithography, as common photosensitive resist materials and associated solvents used in conventional electronics that employ semiconductor substrates dissolve many of the organic semiconductors that are desirably utilized.
As a result, patterning methods other than photolithography must be utilized to manufacture devices which contain organic semiconductor materials. Many of these methods have undesirable traits, which result in high production costs, low device throughput, and low production yield. Additionally, some methods may be restrictive in their compatibility with some materials, resulting in the use of alternative materials which may have performance traits that are less desirable.
One method to manufacture devices which contain organic semiconductor materials employs the use of fine metal masks with physical vapor deposition. The large area mask must be aligned to the underlying substrate prior to each deposition, which reduces throughput. These masks may expand and contract during film deposition, resulting in misalignment of film layers between device components over the large area substrate. When large masks are used to process large substrates, they may sag under their own weight, resulting in device feature misalignment. Mask sagging may be reduced with a vertical mask geometry, but this process may require additional substrate handling and highly customized source delivery systems, increasing production costs and reducing production throughput. The masks must be cleaned and replaced periodically, increasing production costs and reducing machine uptime.
Another method to manufacture devices which contain organic semiconductor materials employs the use of printheads, which may selectively deposit material over a small area. Large area substrates may be selectively coated by scanning one or more printheads. The printheads serially scan the substrate, resulting in patterned films. The scanning process may be slow, reducing process throughput. Using multiple printheads may increase the deposition rate, but each printhead may differentially degrade in deposition performance, resulting in functional non-uniformities over the substrate area. Material delivery may be achieved by a number of methods all of which dissolve desirably patterned materials in a solvent. However, solvents may degrade performance if they contribute impurities that do not evaporate away from the substrate. If deposited in liquid form, the liquid may flow, resulting in deposition non-uniformities. Substrates that, have been patterned in a previous step to have physical wells or areas of surface energy to increase deposition uniformity have been utilized, but these methods may not be compatible with all substrates and require additional processing steps, which may increase manufacturing cost. Devices which require multiple patterned films which cannot be deposited through the printhead in a single step must utilize solvents in subsequent printing steps which will not dissolve the already patterned films. Such restrictions on solvent requirements may exclude the use of certain materials to be desirably patterned and may require the use of more expensive solvents, which may either degrade device performance or increase production cost. If deposited in solid form through local evaporation at the printhead, the printhead and substrate may have to dissipate a large amount of thermal energy, reducing production throughput and increasing cost. This process may also result in device performance that is inferior to devices fabricated by alternate means, such as fine metal masked physical vapor deposition, resulting in undesired performance traits. Alternative materials may be utilized that do not show a difference between the two production processes, but these materials may not result in end device performance that is superior to alternative patterning methods.
Another method to manufacture devices which contain organic semiconductor materials employs the use of materials that are uniformly pre-coated on a secondary substrate which are then selectively transferred to the production substrate by means of a localized energy beam, such as a laser, which induces local vaporization. The laser or optical steering components are scanned over the secondary substrate, resulting in patterned films. This process may also result in device performance that is inferior to devices fabricated by alternate means, such as fine metal masked physical vapor deposition, resulting in undesired product traits. Alternative materials may be utilized that do not show a difference between the two production processes, but these materials may not result in end device performance that is superior to alternative patterning methods. The scanning process may be slow, reducing process throughput. Using multiple lasers or steering components may increase the deposition rate, but each laser may differentially fluctuate in intensity, resulting in deposition non-uniformities and functional non-uniformities over the substrate area.
Another method to manufacture devices which contain organic semiconductor materials employs the use of patterned cylinders for selective deposition, such as offset lithography, rotogravure, and relief printing. A pre-patterned cylinder is inked with the desirably patterned material dissolved in a suitable solvent. The cylinder is rolled over the substrate, resulting large areas of patterned substrates. Cylinder transfer of inks requires the use of solvents, which may degrade performance if they contribute impurities that do not evaporate away from the substrate. On certain substrates, the deposited ink may flow, resulting in deposition non-uniformities. Substrates can have been patterned in a previous step to have physical wells or areas of surface energy to increase deposition uniformity, but these methods may not be compatible with all substrates and require additional processing steps, which may increase manufacturing cost. Devices which require multiple patterned films which cannot be deposited by the cylinder in a single step must utilize solvents in subsequent printing steps which will not dissolve the already patterned films. Such restrictions due to solvent requirements may exclude the use of certain materials to be desirably patterned and may require the use of more expensive solvents, which may either degrade device performance or increase production cost.
Another method to manufacture devices which contain organic semiconductor materials employs the use of specialized materials which may be dissolved and deposited using solvents but whose active material undergoes a photochemical reaction which renders the material insolvent to solvents used in subsequent processing steps. These specialized materials typically result in devices with performance traits that are inferior to devices formed by alternate means and materials, resulting in undesired product traits.
Another method to manufacture devices which contain organic semiconductor materials employs the use of lasers to selectively ablate material which has previously been blanket deposited through some other means. This method may leave undesirable residues on the substrate, contributing to reduced device performance.
U.S. Pat. No. 7,282,430 issued to Karg in 2007 discloses an arrangement for patterning materials for use in large area electronics. A functional material is liquefied under high pressure and temperature in a chamber. The liquid is ejected through a printhead controlled by, for instance, a piezo element. The ejected liquid solidifies on a substrate through freezing which is controlled to maintain a temperature lower than the temperature of the liquid in the printhead. The printhead or substrate is serially scanned, forming a pattern of solid material on the substrate. No solvents are utilized in this process. Unlike the instant invention, there is no resist material and no lift-off step in the process. The instant invention is subtractive, where material is selectively removed from the substrate unlike U.S. Pat. No. 7,282,430, which selectively adds material to the substrate. While both the instant invention and U.S. Pat. No. 7,282,430 employ phase change to result in selective patterning, U.S. Pat. No. 7,282,430 describes phase changes between liquid and solid, where the instant invention describes phase changes between vapor and solid phases.
In 1992, Cuomo disclosed a method to pattern films with a vaporizable mask (“Selective Deposition With “Dry” Vaporizable Lift-off Mask,” IBM Technical Disclosure Bulletin, vol 35, No. 1A, pp. 75-76, June 1992). A condensable vapor of either water, acetone, or chlorobenzene is uniformly coated onto a substrate forming a lift-off mask. The mask is spatially patterned with a pulsed laser incident through a projection mask through selective ablation. The substrate and patterned mask is uniformly coated with a second material by sputtering or evaporation. The composite is warmed by any of a variety of means to lift off the mask and overlying material, transferring a pattern to the second material. Unlike the instant invention, spatial patterning is communicated by a pulsed laser incident through a projection mask. Projection masks do not remedy deficiencies related to time consuming alignment between a mask and the substrate. A lift-off mask comprised of water, acetone, or chlorobenzene will dissolve certain materials desirably used in large area electronic devices which utilize organic semiconductors and do not have utility in patterning elements of such devices.
In 1978, Johnson disclosed a method for in situ lithography (“Condensed Gas, In Situ Lithography,” IBM Technical Disclosure Bulletin, vol 20, No. 9, pp. 3737-3738, February 1978). A condensable vapor is uniformly coated onto a wafer forming a condensed gas resist (CGR). The CGR is spatially patterned using local heat application from light beams (preferably lasers), electron beams, or microwaves which are absorbed by the wafer, or from lines on the wafer. The wafer and patterned CGR is uniformly coated with a second material. The temperature of the entire wafer is raised above the CGR boiling point, which serves to liquify the CGR from its solidified state, which is followed by boiling to remove both the CGR and the overlying material, transferring the pattern in the CGR to the second material. Unlike the instant invention, the process is intended for use with wafers. Semiconductor wafers may be strongly absorptive of light beams, providing a convenient means of selectively patterning the CGR. The instant invention applies to non-semiconductor substrates such as glass, plastic, metal foil, or ceramic which are suitable for large area electronic devices for use in applications where semiconductor substrates are too expensive for economically viable products. The process employs two phase changes for resist lift-off, solid to liquid and liquid to vapor, in contrast to the instant invention which employs a single phase change from solid to vapor for resist lift-off. Utilizing liquid boiling of the CGR diminishes the achievable resolution of the desirably patterned film since the liquid CGR will flow to some degree no matter how short the residence time the CGR exists as a liquid. In addition, utilizing liquid phase CGRs may increase residue formation on the substrate, increase liquid surface tension effects and increase waste products of the process.
U.S. Pat. No. 7,435,353 issued to Golovchenko in 2008 and U.S. Pat. No. 7,524,431 issued to Branton in 2009 describe processes to form high resolution patterned material layers on a structure. A vapor is condensed to a solid condensate layer on a surface of the structure and then selected nano-metrically patterned and nano-scale regions of the condensate layer are locally removed by directing electron beams at the selected regions, exposing the structure at the selected regions. A material layer is then deposited on top of the solid condensate layer and the exposed structure at the selected regions. The solid condensate layer and regions of the material layer that were deposited on the solid condensate layer are then removed, leaving a patterned material layer on the structure. The process is related to electron beam lithography, where nano-scale patterns are transferred to a resist for nano-scale electronic, mechanical and chemical devices. The process employs either one scanned electron beam or multiple energy beams to selectively pattern the condensate layer in contrast to the instant invention, which utilizes either a single laser beam, resistive heating from patterned line on the underlying substrate, or a stamp with raised features brought into thermal contact with the condensate layer. Due to the slow nature to electron beam scanning, the processes described in U.S. Pat. Nos. 7,435,353 and 7,524,431 are applicable to nano-scale features and patterns and are not readily scalable to larger feature sizes in excess of 5 micrometers in contrast to the instant invention, directed towards the manufacture of large area electronic devices with features in excess of 5 micrometers distributed over substrates with lateral dimensions from 100 to 3000 centimeters in length or width.
U.S. Pat. No. 7,759,609 issued to Asscher in 2010 describes a method for forming nano-patterns of a material on a substrate called buffer layer assisted laser patterning. A layered structure is formed on the substrate, this layered structure being in the form of spaced-apart regions of the substrate defined by the pattern to be formed, each region including a weakly physisorbed buffer layer and a layer of the material to be patterned on top of the buffer layer. A thermal process is then applied to the layered structure to remove the remaining buffer layer in said regions, and thus form a stable pattern of said material on the substrate resulting from the buffer layer assisted laser patterning. The method may utilize either positive or negative lithography. The patterning may be implemented using irradiation with a single uniform laser pulse via a standard mask used for optical lithography. The positive lithography process utilizes laser pulsed patterning of the composite of buffer (resist) and overlying material which is deposited via soft landing following laser ablation of the buffer layer, in contrast to the instant invention whereupon a patterned condensate resist is coated with uniform material which is subsequently removed. The negative lithography process utilizes pulsed laser radiation to pattern the buffer and utilizes laser ablation to lift off the buffer, in contrast to the instant intention which utilizes a thermal shock induced by temperature change to lift off the resist material. The negative lithography process described in U.S. Pat. No. 7,759,609 is suited for forming narrow lines of less than 30 nanometers, in contrast to the instant invention directed towards the manufacture of large area electronics with feature sizes greater than 5000 nanometers,
German patent DE 4318663 C1 issued to Holdermann in 1994 describes a process to form patterned films. Water ice forms a solid layer on a semiconductor substrate and then regions of the water ice layer are exposed to localized heating through various means, removing the water ice at the selected regions. A desirably patterned film is formed by either plating or etching the regions not covered in water ice. The plating or etching is performed in a liquid solution maintained below 0 C, such that the water ice does not melt or vaporize. The solid water ice layer is then removed, leaving a patterned material layer on the structure. The process described in DE 4318663 C1 selectively etches or plates the desirably patterned material in contrast to the instant invention, which utilizes blanket deposition followed by a lift-off process step. The process described in DE 4318663 C1 utilizes water ice and may include water vapor and/or liquid water. The instant invention is directed towards the use of non-water condensate resists for the patterning of films comprised of materials which are sensitive and reactive to water to the degree that water is desirably limited to levels much less than 1 part per billion.
U.S. Pat. No. 4,535,023 issued to Whitlock in 1985 describes a process to pattern a target for x-ray lasing. A substrate is placed in a gaseous atmosphere of a second material held at a temperature below the condensation point of the second material, such that the second material forms a condensed film on the substrate. The film is selectively heated using masked light beams to vaporize areas of the condensed film. The condensed film is not removed but forms an active component of the laser. The process described in U.S. Pat. No. 4,535,023 is directed towards the fabrication of targets for x-ray lasing made out of, for instance, sodium and neon. In contrast, the instant invention is directed towards the fabrication of large area electronics containing organic semiconductor films. The process described in U.S. Pat. No. 4,535,023 utilizes a patterned condensed film as an active device component which is not followed by subsequent deposition steps, whereas in the instant invention the condensed film functions as a sacrificial layer to lift-off a subsequently uniformly deposited film.
European patent document EP 0233747 published by Woods in 1987 describes a process to apply a polymeric resist coating of high molecular weight to a substrate. The process exposes a substrate to a vapor of an anionically polymerizable monomer which then polymerizes on the substrate, which then can be useful as a resist coating in lithographic processes employing plasma or acid etching. The process described in EP 0233747 relates to polymerizable condensable materials, in contrast to the instant invention directed towards simple molecular or elemental materials which do not form polymers or undergo any chemical reactions following condensation on the substrate. The process described in EP 0233747 utilizes a patterned resist as a blocking layer for a selective etching process, whereas in the instant invention the condensed film functions as a sacrificial layer to lift-off a subsequently uniformly deposited film
U.S. Pat. No. 4,348,473 issued to Okumura in 1982 relates to a method for the preparation of microelectronic device which comprises a series of process steps performed on a substrate in a single vacuum chamber. A substrate is coated with a monomer film which is subsequently polymerized following the exposure to a light or electron beam. The selectively polymerized film is then uniformly heated to vaporize the monomer regions; the patterned polymer is used as a resist during a subsequent etching step and removed thereafter. The process described in U.S. Pat. No. 4,348,473 is directed toward polymerizable resist materials, in contrast to the instant invention directed towards simple molecular or elemental materials which do not form polymers or undergo any chemical reactions following condensation on the substrate. The process described in U.S. Pat. No. 4,348,473 utilizes a patterned resist as a blocking layer for a selective etching process, whereas in the instant invention the condensed film functions as a sacrificial layer to lift off a subsequently uniformly deposited film.